1. Field of the Invention
The present invention relates to methods of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like and forming a chemical casing in a well bore penetrating the weak zones or formations while drilling the well bore.
2. Description of the Prior Art
Rotary drilling methods are commonly utilized in the drilling of oil and gas wells. That is, the well bore which extends from the surface into one or more subterranean oil and/or gas producing formations is drilled by a rotary drilling rig on the surface which rotates a drill bit attached to a string of drill pipe. The drill bit includes rotatable cutting surfaces so that when the drill bit is rotated by the drill string against subterranean strata under pressure a bore hole is produced.
A drilling fluid is circulated downwardly through the drill string, through the drill bit and upwardly in the annulus between the walls of the well bore and the drill string. The drilling fluid functions to maintain hydrostatic pressure on formations penetrated by the well bore and to remove cuttings from the well bore. As the drilling fluid is circulated, a filter cake of solids from the drilling fluid forms on the walls of the well bore. The filter cake build-up is a result of initial fluid loss into permeable formations and zones penetrated by the well bore. The presence of the filter cake reduces additional fluid loss as the well is drilled.
In addition to removing cuttings from the well bore and forming filter cake on the well bore, the drilling fluid cools and lubricates the drill bit and exerts a hydrostatic pressure against the well bore walls to prevent blow-outs, i.e., to prevent pressurized formation fluids from flowing into the well bore when formations containing the pressurized fluids are penetrated. The hydrostatic pressure created by the drilling fluid in the well bore may fracture low mechanical strength formations penetrated by the well bore which allows drilling fluid to be lost into the formations. When this occurs, the drilling of the well bore must be stopped and remedial steps taken to seal the fractures which are time consuming and expensive.
In order to insure that fracturing of low mechanical strength formations penetrated by the well bore and other similar problems do not occur, it has heretofore been the practice to intermittently seal the well bore by cementing pipe referred to in the art as casing or liners in the well bore. The points in the well bore during its drilling at which the drilling is stopped and casing or liners are installed in the well bore are commonly referred to as xe2x80x9ccasing pointsxe2x80x9d. Casing or a liner is placed in the well bore above each casing point and a sealing composition such as a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surface of the casing or liner disposed therein. The hydraulic cement composition is permitted to set in the annulus thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. This technique of cementing pipe in the well bore as the drilling progresses has a number of disadvantages including the time and expense incurred in placing and sealing the pipe as well as the reduction in the well diameter after each casing point. That is, the well diameter must be reduced below each casing point so that a smaller casing can be lowered through the previously placed casing and sealed in the well bore.
Another problem that occurs in the drilling and completion of well bores is that when the well bore is drilled into and through unconsolidated weak zones or formations formed of clays, shales, sand stone and the like, unconsolidated clay, shale and sand slough off the sides of the well bore which enlarges the well bore and often causes the drill bit and drill pipe to become stuck whereby drilling must be stopped and remedial steps taken.
Thus, there are needs for improved methods of drilling well bores whereby unconsolidated weak zones or formations are consolidated and the mechanical strength of the well bore is increased during drilling without the need to stop drilling for prolonged periods of time.
By the present invention, methods of consolidating unconsolidated weak zones or formations during drilling are provided. Also, methods of forming a hard and tough chemical casing in a well bore during drilling to increase the mechanical strength of the well bore are provided. The chemical casing formed while drilling also prevents undesirable migration of fluid between zones or formations penetrated by the well bore, generally referred to as xe2x80x9czonal isolation.xe2x80x9d The methods of consolidating unconsolidated weak zones or formations during drilling or forming a hard and tough chemical casing during drilling can be carried out separately or simultaneously.
A method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
Another method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is comprised of the following steps. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water and a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like. Thereafter, the well bore is contacted with a treating fluid having a pH in the range of from about 6 to about 10 and comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
A method of this invention for forming a chemical casing in a well bore to improve the mechanical strength thereof and/or prevent undesirable migration of fluids between zones or formations while drilling the well bore is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a water soluble or water dispersible polymer which is cross-linkable by thermoset resins and causes the resins to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin, and a delayed dispersible acid catalyst for curing the solid thermoset resin and the water soluble thermoset resin, the drilling fluid forming a filter cake on the walls of the well bore that cures into a hard and tough cross-linked chemical casing thereon.
A method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore and/or prevent undesirable migration of fluids between zones or formations while drilling the well bore is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin and a delayed dispersible acid catalyst for curing the thermoset resins, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented and forms a hard and tough cross-linked chemical casing on the walls of the well bore which prevents the undesirable migration of fluids between zones or formations.
Another method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore while drilling the well bore is comprised of the following steps. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10 and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a particulate curable solid thermoset resin and a delayed acid catalyst for curing the solid thermoset resin, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented. Thereafter, the well bore is contacted with a treating fluid comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin, the treating fluid components depositing on the filter cake formed by the drilling fluid and the thermoset resin curing into a hard and tough cross-linked chemical casing on the walls of the well bore.
The objects, features and advantages of the invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
The present invention provides methods of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing, methods of forming a hard and tough cross-linked chemical casing in a well bore while drilling the well bore which increases the mechanical strength of the well bore and provides zonal isolation and methods of both consolidating unconsolidated weak zones or formations penetrated by a well bore and forming a hard and tough cross-linked chemical casing in the well bore while drilling the well bore.
Unstable materials such as clays, shales, sand stone and the like make up a high percentage of the formations in which wells are drilled, and a majority of well bore problems are a result of the instability of such materials, particularly shale instability. Shales are sedimentary rocks that contain a variety of clays. Shales containing montmorillonite, often referred to as smectite clays, swell and disperse when contacted by water. Shales which swell upon contacting water are often referred to as heaving or sloughing shales. Such shales upon contact with aqueous drilling fluids swell and fracture rendering the well bore wall unstable. In such cases, the well bore wall sloughs into the well bore. Sloughing of shale and other similar unstable materials into the well bore can cause the drill string to become stuck and can enlarge the well bore resulting in large subterranean cavities. Additionally, when sloughing occurs while the drill bit is being changed at the surface, the well bore fills up and must be cleared before drilling can proceed. Furthermore, the heaving unstable material suspended in the drilling fluid increases its solid content, and as a result, the viscosity of the drilling fluid increases to the point where the drilling fluid must be chemically treated to reduce its viscosity or it must be diluted followed by the addition of weighting material to maintain its mud weight. The instability of clays, shales, sand stone and the like is also caused by hydraulic pressure differential leading to fluid transport and by pressure changes near the well bore as the drilling fluid compresses pore fluid and diffuses a pressure front into the formation. The chemicals and other materials used in accordance with the present invention prevent swelling and dispersion of unstable materials, reduce pressure transmission from the well bore fluids and prevent drilling fluid penetration into the unstable materials by building an impenetrable lining at the unstable material/well bore interface.
Consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore prevents sloughing of the clays, shales, sand stone and the like into the well bore and prevents the need for implementing time consuming and costly remedial steps. The formation of a hard and tough chemical casing in a well bore while the well bore is being drilled increases the mechanical strength of the well bore whereby hydrostatic pressure exerted on the well bore by the drilling fluid does not cause fractures or the like to occur in the well bore. Such fractures cause drilling fluid to be lost and also require stoppage of the drilling operation and costly remedial steps to be taken. Another significant advantage of increasing the mechanical strength of the well bore by forming a hard and tough chemical casing thereon is the reduction or elimination of casing points at which casing or liners are cemented in the well bore which reduces or eliminates the overall time and cost of cementing the well. An additional advantage is that the well bore has a larger diameter in the production zone due to fewer casing points which increases productivity.
A method of the present invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing comprises drilling the well bore with a drilling fluid having a pH in the range of from about 6 to about 10, preferably about 8. The drilling fluid is comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
The water utilized to form the drilling fluid can be fresh water, unsaturated salt solutions or saturated salt solutions, including brine and seawater. Generally, water from any source can be utilized so long as it doesn""t adversely react with components of the drilling fluid.
Examples of polymeric cationic catalysts capable of accepting and donating protons which are adsorbed on clays, shales, sand stone and the like include, but are not limited to, polyethyleneimine, poly(dimethylaminoethylmethacrylate) and poly(dimethylaminopropylmethacrylate). Of these, polyethyleneimine is preferred. The polymeric cationic catalyst is generally included in the drilling fluid in an amount in the range of from about 1% to about 15% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 2% to about 10% by weight of the water and most preferably in an amount of about 6%.
The water soluble or dispersible polymers which are cross-linked by the thermoset resins utilized in accordance with this invention are polymers containing one or more of hydroxyl, amide, carboxyl and epoxy functional groups. Examples of such polymers include, but are not limited to, acrylic latexes, polyvinylalcohol, polyvinylbutyral, polyesters, polyalkylacrylic acids, polyurethanes, acrylamide polymers, proteins, polyols and polysaccharides such as chitosan, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, water soluble starches, guar gum, xanthan gum, welan gum, carragenan gum and arabic gum. Of these, polysaccharides are preferred. The water soluble or dispersible polymer which is cross-linked by thermoset resins is generally included in the drilling fluid in an amount in the range of from about 0.5% to about 20% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 1% to about 10% by weight of the water and most preferably in an amount of about 3%.
The water soluble or dispersible thermoset resins (including particulate solid thermoset resins having a particle size in the range of from about 50 to about 1000) utilized in accordance with this invention are selected from melamine-formaldehyde type resins, i.e., amino resins made from melamine and formaldehyde, urea-formaldehyde type resins, i.e., amino resins made from urea and formaldehyde and phenol-formaldehyde type resins, i.e., synthetic thermoset resins made from phenol and formaldehyde. More preferably, the thermoset resins utilized are selected from alkyl ethers of melamine-formaldehyde resins and alkyl ethers of urea-formaldehyde resins. Of these, alkyl ethers of melamine-formaldehyde resins are preferred. An alkyl ether of melamine-formaldehyde resin which is particularly suitable is commercially available under the tradename xe2x80x9cASTRO MEL CR1(trademark)xe2x80x9d from Borden Chemical of Springfield, Oreg., USA. The water soluble or dispersible thermoset resin utilized in the above described method is generally present in the drilling fluid in an amount in the range of from about 5% to about 80% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 20% to about 70% by weight of water and most preferably in an amount of about 50%.
The thermoset resins described above, when catalyzed by heat, catalysts or other means, form substantially infusible or insoluble materials which do not soften on reheating. When cross-linked and cured, the thermoset polymers are strong, hard and tough.
As will be understood by those skilled in the art, the drilling fluids of this invention can include other conventional components such as weighting materials, viscosifiers, dispersants and fluid loss control agents.
Another method of this invention for consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is comprised of the following steps. The well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10, preferably 8, and is comprised of water and a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like. Thereafter, the well bore is contacted with a treating fluid having a pH in the range of from about 6 to about 10, preferably 8, and comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented.
The components of the drilling fluid and treating fluid of the above described method, i.e., the water, the polymeric cationic catalyst, the water soluble or dispersible polymer which is cross-linkable by a thermoset resin and the water soluble or dispersible thermoset resin are the same as those previously described.
The polymeric cationic catalyst is present in the drilling fluid in a general amount in the range of from about 1% to about 15% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 2% to about 10% by weight of the water and most preferably in an amount of about 6%.
The water soluble or dispersible polymer which is cross-linked by a thermoset resin is present in the treating fluid in a general amount in the range of from about 0.5% to about 20% by weight of water in the treating fluid, more preferably in an amount in the range of from about 1% to about 10% of the water and most preferably in an amount of about 3%. The water soluble or dispersible thermoset resin is present in the treating fluid in a general amount in the range of from about 5% to about 80% by weight of the water and most preferably in an amount of about 50%.
The drilling fluid as well as the treating fluid can also include other additives which are well known to those skilled in the art such as weighting materials, viscosifiers, dispersants and fluid loss control agents.
The first method described above which utilizes a single fluid for drilling the well bore and simultaneously consolidating weak zones or formations is utilized at locations where it is known that unconsolidated weak zones and formations will be encountered. The second method described above which utilizes both a drilling fluid and a treating fluid is used in drilling applications where it is unknown if unconsolidated weak zones or formations will be encountered. In the second method, if unconsolidated weak zones or formations are not encountered, the treating fluid step is not required and the time and expense required for performing the treating fluid step will be saved.
A method of this invention for forming a chemical casing in a well bore for improving the mechanical strength thereof and provide zonal isolation to prevent fluid flow between zones or formations while drilling the well bore is as follows. The well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10, preferably 8. The drilling fluid is comprised of water, a water soluble or water dispersible polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin, and a delayed dispersible acid catalyst for curing the solid thermoset resin and the water soluble thermoset resin. The drilling fluid components form a filter cake on the walls of the well bore that cures into a hard and tough cross-linked chemical casing thereon.
The water soluble or dispersible polymer which is cross-linked by a thermoset resin is selected from the group consisting of polymers containing one or more of hydroxyl, amide, carboxyl and epoxy functional groups. Examples of such polymers include, but are not limited to, acrylic latexes, polyvinylalcohol, polyvinylbutyral, polyesters, polyalkylacrylic acids, polyurethanes, acrylamide polymers, proteins, polyols and polysaccharides such as chitosan, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, water soluble starches, guar gum, xanthan gum, welan gum, carragenan gum and arabic gum. The polymer is included in the drilling fluid in an amount in the range of from about 0.5% to about 20% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 1% to about 10% by weight of water and most preferably in an amount of about 3%.
As mentioned above, the particulate curable solid thermoset resin has a particle size in the range of from about 50 to about 1000 microns and is selected from particulate solid melamine-formaldehyde type resins, urea-formaldehyde type resins or phenol-formaldehyde type resins, and more preferably from particulate solid alkyl esters of melamine-formaldehyde resins and particulate solid alkyl esters of urea-formaldehyde resins. Of these, the particulate solid alkyl esters of melamine-formaldehyde resins are preferred. The particulate curable solid thermoset resin used is included in the drilling fluid in the general amount in the range of from about 5% to about 50% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 10% to about 30% by weight of water and most preferably in an amount of about 15%.
The water soluble thermoset resin is selected from water soluble melamine-formaldehyde type resins, urea-formaldehyde type resins or phenol-formaldehyde type resins, and more preferably from water soluble alkyl ethers of melamine-formaldehyde resins and water soluble alkyl ethers of urea-formaldehyde resins. Of these, water soluble alkyl ethers of melamine-formaldehyde resins are preferred. The water soluble thermoset resin used is included in the drilling fluid in an amount in the range of from about 5% to about 80% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 20% to about 70% by weight of water and most preferably in an amount of about 50%.
The acid in the delayed dispersible acid catalyst is an organic or inorganic acid selected from the group consisting of p-toluene sulfonic acid, dinonylnaphthalene sulfonic acid, dodecyl benzene sulfonic acid, oxalic acid, maleic acid, hexamic acid, a copolymer of phthalic and acrylic acid, trifluoromethane sulfonic acid, phosphoric acid, sulfuric acid, hydrochloric acid, sulfamic acid and ammonium salts that produce acids when dissolved in water. Of these, ammonium chloride is preferred. The acid in the delayed acid utilized is included in the drilling fluid in a general amount in the range of from about 0.5% to about 8% by weight of thermoset resin in the drilling fluid, more preferably in an amount in the range of from about 1% to about 6% by weight of resin and most preferably in an amount of about 4%.
The acid utilized can be delayed using various techniques known to those skilled in the art. A preferred technique for controlling the release of the acid catalyst utilized in the present invention is to cause the acid to be absorbed into a particulate porous solid material whereby the acid is encapsulated. When the encapsulated acid is combined with the drilling fluid, it is slowly released into the drilling fluid. While a variety of porous solid materials can be utilized, particularly suitable such materials are inorganic porous solid materials which remain dry and free flowing after absorbing a liquid chemical additive therein. Examples of such porous solid materials include, but are not limited to, metal oxides, e.g., silica and alumina; metal salts of alumina-silicates, e.g., zeolites, clays and hydrotalcites; and others. Of the various particulate porous solid materials that can be used, particulate porous silica is preferred with precipitated silica being the most preferred.
The delayed release of a liquid chemical additive absorbed in particulate porous precipitated silica is by osmosis whereby the encapsulated liquid chemical diffuses through the porous solid material as a result of it being at a higher concentration within the porous material than its concentration in the liquid fluid outside the porous material. In order to further delay the release of a liquid chemical additive, the porous precipitated silica can be coated with a slowly soluble coating. Examples of suitable such slowly soluble materials which can be used include, but are not limited to, EDPM rubber, polyvinyldichloride (PVDC), nylon, waxes, polyurethanes, cross-linked partially hydrolyzed acrylics and the like. A more detailed description of the encapsulating techniques described above is set forth in U.S. Pat. No. 6,209,646 issued on Apr. 3, 2001 to Reddy et al., the disclosure of which is incorporated herein by reference thereto.
In order to strengthen the chemical casing formed in the well bore, one or more insoluble reinforcing materials can be included in the drilling fluid. The reinforcing materials become a part of the filter cake deposited on the walls of the well bore that cures into a hard and tough casing thereon. The presence of the reinforcing materials in the strong, hard and tough chemical casing provides additional strength to the chemical casing. The insoluble reinforcing materials which can be utilized include, but are not limited to, carbon fibers, glass fibers, mineral fibers, cellulose fibers, silica, zeolite, alumina, calcium sulfate hemihydrate, acrylic latexes, polyol-polyesters and polyvinyl butyral. Of these, fibrous materials or calcium sulfate hemihydrate are preferred. When used, the reinforcing material is included in the drilling fluid in an amount in the range of from about 2% to about 25% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 5% to about 20% by weight of water and most preferably in an amount of about 10%.
As mentioned above, the drilling fluid can include other conventional drilling fluid additives which are known to those skilled in the art.
A combined method of this invention for both consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and for forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength thereof and/or to provide zonal isolation while drilling the well bore is as follows. A well bore is drilled with a drilling fluid having a pH in the range of from about 6 to about 10, preferably 8. The drilling fluid is comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on the unconsolidated clays, shales, sand stone and the like, a water soluble or dispersible polymer which is cross-linked by a thermoset resin and causes the resin to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin and a delayed dispersible acid catalyst for curing the thermoset resins, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented and forms a hard and tough cross-linked chemical casing on the walls of the well bore.
The polymeric cationic catalyst in the drilling fluid is selected from the group consisting of polyethyleneimine, poly(dimethylaminoethylmethacrylate) and poly(dimethylaminopropylmethacrylate). Of these, polyethyleneimine is preferred. The polymeric cationic catalyst is included in the drilling fluid in an amount in the range of from about 1% to about 15% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 2% to about 10% by weight of water and most preferably in an amount of about 6%.
The water soluble or dispersible polymer which is cross-linked by a thermoset resin utilized in the drilling fluid is selected from polymers containing one or more of hydroxyl, amide, carboxyl and epoxy functional groups. Examples of such polymers include, but are not limited to, acrylic latexes, polyvinylalcohol, polyvinylbutyral, polyesters, polyalkylacrylic acids, polyurethanes, acrylamide polymers, proteins, polyols and polysaccharides such as chitosan, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, water soluble starches, guar gum, xanthan gum, welan gum, carragenan gum and arabic gum. Of these, polysaccharides are preferred. The water soluble or dispersible polymer which is cross-linked by a thermoset resin is generally present in the drilling fluid in an amount in the range of from about 0.5% to about 20% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 1% to about 10% by weight of water and most preferably in an amount of about 3%.
The particulate curable solid thermoset resin which preferably has a particle size in the range of from about 50 to about 1000 microns is selected from particulate solid melamine-formaldehyde type resins, urea-formaldehyde type resins or phenol-formaldehyde resins, and more preferably from particulate solid alkyl ethers of melamine-formaldehyde resins and particulate solid alkyl ethers of urea-formaldehyde type resins. Of these, particulate solid alkyl ethers of melamine-formaldehyde resins are preferred. The particulate curable solid thermoset resin is generally included in the drilling fluid in an amount in the range of from about 5% to about 50% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 10% to about 30% by weight of water and most preferably in an amount of about 15%.
The water soluble thermoset resin is selected from the group consisting of water soluble alkyl ethers of melamine-formaldehyde resins, water soluble alkyl ethers of urea-formaldehyde resins and water soluble phenol-formaldehyde type resins. Of these, a water soluble alkyl ether of melamine-formaldehyde resin is preferred. The water soluble thermoset resin is included in the drilling fluid in an amount in the range of from about 5% to about 80% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 20% to about 70% by weight of water and most preferably in an amount of about 50%.
The acid in said delayed acid catalyst in said drilling fluid is an organic or inorganic acid selected from the group consisting of p-toluene sulfonic acid, dinonylnaphthalene sulfonic acid, dodecyl benzene sulfonic acid, oxalic acid, maleic acid, hexamic acid, a copolymer of phthalic and acrylic acid, trifluoromethane sulfonic acid, phosphoric acid, sulfuric acid, hydrochloric acid, sulfamic acid and ammonium salts that produce acids when dissolved in water. Of these, ammonium chloride acid is preferred. The acid in the delayed acid catalyst utilized is generally present in the drilling fluid in an amount in the range of from about 0.5% to about 8% by weight of the thermoset resin in the drilling fluid, more preferably in an amount in the range of from about 1% to about 6% by weight of resin and most preferably in an amount of about 4%.
The drilling fluid can optionally include an insoluble chemical casing reinforcing material selected from the group consisting of carbon fibers, glass fibers, mineral fibers, cellulose fibers, silica, zeolite, alumina, calcium sulfate hemihydrate, acrylic latexes, polyol-polyesters and polyvinyl butyral. Of these, fibrous materials or calcium sulfate hemihydrate are preferred. When used, the insoluble reinforcing material is generally present in the drilling fluid in an amount in the range of from about 2% to about 25% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 5% to about 20% by weight of water and most preferably in an amount of about 10%.
As mentioned above, the drilling fluid can also include conventional additives known to those skilled in the art.
Another method of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore and/or to provide zonal isolation while drilling the well bore is comprised of the steps of: (a) drilling the well bore with a drilling fluid having a pH in the range of from about 6 to about 10, preferably 8, and comprised of water, a polymeric cationic catalyst capable of accepting and donating protons which is adsorbed on said unconsolidated clays, shales, sand stone and the like, a particulate curable solid thermoset resin and a delayed acid catalyst for curing the solid resin, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented; and (b) contacting the well bore with a treating fluid comprised of water, a water soluble or dispersible polymer which is cross-linkable by a thermoset resin and causing the resin to be hard and tough when cured and a water soluble or dispersible thermoset resin, the treating fluid components depositing on the filter cake formed in step (a) and the thermoset resins curing into a hard and tough cross-linked chemical casing on the walls of the well bore.
The components in the drilling fluid and the treating fluid are the same as the components described above in connection with the preceding method.
The polymeric cationic catalyst is generally present in the drilling fluid in an amount in the range of from about 2% to about 25% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 5% to about 20% by weight of water and most preferably in an amount of about 10%.
The particulate curable solid thermoset resin is generally present in the drilling fluid in an amount in the range of from about 5% to about 50% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 10% to about 30% by weight of water and most preferably in an amount of about 15%.
The acid in the delayed acid catalyst is generally present in the drilling fluid in an amount in the range of from about 0.5% to about 8% by weight of the thermoset resin in the drilling fluid, more preferably in an amount in the range of from about 1% to about 6% by weight of water and most preferably in an amount of about 4%.
The water soluble or dispersible polymer which is cross-linkable by a thermoset resin is generally present in the treating fluid in an amount in the range of from about 0.5% to about 20% by weight of water in the treating fluid, more preferably in an amount in the range of from about 1% to about 10% by weight of water and most preferably in an amount of about 3%.
The water soluble or dispersible thermoset resin is generally present in the treating fluid in an amount in the range of from about 5% to about 80% by weight of water in the drilling fluid, more preferably in an amount in the range of from about 20% to about 70% by weight of water and most preferably in an amount of about 50%.
The drilling fluid can optionally include a reinforcing material to strengthen the chemical casing as described above in connection with the preceding method. When used, the reinforcing material is generally included in the drilling fluid in an amount in the range of from about 5% to about 50%, more preferably in an amount in the range of from about 10% to about 30% by weight of water and most preferably in an amount of about 15%.
As mentioned, the drilling fluid can also include conventional additives known to those skilled in the art.
A preferred method of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing is comprised of drilling the well bore with a drilling fluid having a pH of about 8 and comprised of water, a cationic polyethyleneimine catalyst which is adsorbed on said unconsolidated clays, shales, sand stone and the like present in the drilling fluid in an amount in the range of from about 2% to about 10% by weight of water in the drilling fluid, a polysaccharide polymer which is capable of being cross-linked by a thermoset resin and causing the resin to be hard and tough when cured present in an amount in the range of from about 1% to about 10% by weight of water in the drilling fluid and an alkyl ether of a melamine-formaldehyde thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented present in the drilling fluid in an amount in the range of from about 20% to about 70% by weight of water in the drilling fluid.
Another preferred method of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like while drilling a well bore penetrating the zones or formations to prevent sloughing comprises the steps of: (a) drilling the well bore with a drilling fluid having a pH of about 8 and comprised of water, a cationic polyethyleneimine catalyst which is adsorbed on the unconsolidated clays, shales, sand stone and the like present in the drilling fluid in an amount in the range of from about 2% to about 10% by weight of the drilling fluid; and then (b) contacting the well bore with a treating fluid having a pH of about 8 comprised of water, a polysaccharide polymer which is capable of being cross-linked by a thermoset resin and causing the resin to be hard and tough when cured present in an amount in the range of from about 1% to about 10% by weight of water in the treating fluid and an alkyl ether of a melamine-formaldehyde thermoset resin which cross-links the polymer, is catalyzed and cured by the catalyst and consolidates the weak zones or formations so that sloughing is prevented present in an amount in the range of from about 20% to about 70% by weight of water in the treating fluid.
A preferred method of this invention for forming a chemical casing in a well bore to improve the mechanical strength thereof and provide zonal isolation while drilling the well bore is comprised of drilling the well bore with a drilling fluid having a pH of about 8 and comprised of water, a water soluble or water dispersible polymer which is capable of being cross-linked by a thermoset resin and causing the resin to be hard and tough when cured present in the drilling fluid in an amount in the range of from about 1% to about 10% by weight of water in the drilling fluid, a particulate curable solid alkyl ether of a melamine-formaldehyde thermoset resin present in the drilling fluid in an amount in the range of from about 10% to about 30% by weight of water in the drilling fluid, a water soluble alkyl ether of a melamine-formaldehyde thermoset resin present in the drilling fluid in an amount in the range of from about 20% to about 70% by weight of water in the drilling fluid, and a dispersible delayed ammonium chloride acid catalyst for curing the solid thermoset resin and the water soluble thermoset resin present in the drilling fluid in an amount in the range of from about 1% to about 6% by weight of thermoset resin in the drilling fluid, the drilling fluid forming a filter cake on the walls of the well bore that cures into a hard and tough cross-linked chemical casing thereon.
A preferred method of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength thereof and/or to provide zonal isolation while drilling the well bore is comprised of drilling the well bore with a drilling fluid having a pH of about 8 and comprised of water, a cationic polyethyleneimine catalyst which is adsorbed on the unconsolidated clays, shales, sand stone and the like present in an amount in the range of from about 2% to about 10% by weight of water in the drilling fluid, a water soluble or dispersible polysaccharide polymer which is cross-linkable by a thermoset resin and causes the resin to be hard and tough when cured present in the drilling fluid in an amount in the range of from about 1% to about 10% by weight of water in the drilling fluid, a particulate curable solid alkyl ether of melamine-formaldehyde thermoset resin present in an amount in the range of from about 10% to about 30% by weight of water in the drilling fluid, a water soluble alkyl ether of melamine-formaldehyde thermoset resin present in an amount in the range of from about 20% to about 70% by weight of water in the drilling fluid and a dispersible delayed ammonium chloride acid catalyst for curing the thermoset resins present in the drilling fluid in an amount in the range of from about 1% to about 6% by weight of thermoset resin in the drilling fluid, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented and forms a hard and tough cross-linked chemical casing on the walls of the well bore.
Another preferred method of consolidating unconsolidated weak zones or formations formed of clays, shales, sand stone and the like to prevent sloughing and forming a chemical casing in a well bore penetrating the weak zones or formations to improve the mechanical strength of the well bore and/or to provide zonal isolation while drilling the well bore is comprised of the steps of: (a) drilling the well bore with a drilling fluid having a pH of about 8 and comprised of water, a cationic polyethyleneimine catalyst which is adsorbed on the unconsolidated clays, shales, sand stone and the like present in an amount in the range of from about 2% to about 10% by weight of water in the drilling fluid, a particulate curable solid alkyl ether of melamine-formaldehyde thermoset resin present in an amount in the range of from about 10% to about 30% by weight of water in the drilling fluid and a delayed ammonium chloride acid catalyst for curing the solid resin present in the drilling fluid in an amount in the range of from about 1% to about 6% by weight of thermoset resin in the drilling fluid, the drilling fluid forming a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented; and (b) contacting the well bore with a treating fluid comprised of water, a water soluble or dispersible polysaccharide polymer which is capable of being cross-linked by a thermoset resin and causing the resin to be hard and tough when cured present in the treating fluid in an amount in the range of from about 1% to about 10% by weight of water in the treating fluid, a water soluble or dispersible alkyl ether of melamine-formaldehyde thermoset resin present in the treating fluid in an amount in the range of from about 20% to about 70% by weight of water in the treating fluid, the treating fluid components depositing on the filter cake formed in step (a) and the thermoset resins curing into a hard and tough cross-linked chemical casing on the walls of the well bore.
In order to further illustrate the methods of this invention, the following examples are given.